The invention refers to a method and a device for agglomerating particles in a gaseous flow through an acoustical agglomeration chamber.
Solid and liquid particles produced by different industrial processes and discharged to ambience by means of a gaseous flow constitute a source of pollution for nature and may be a risk for the health of men. In particular the submicron particle concentration in the atmosphere seems to be the cause of an increasing human disease rate. Thus the invention aims to conceive a method and a device which allows to reduce in particular the submicron particle rate in a gaseous flow before the latter is discharged to the atmosphere.
The state of the art comprises filters for gaseous flows which apply either electrostatic fields or mechanical processes (separators of the cyclone or venturi type) which are rather complex or ensure only a limited purification efficiency, especially if submicron particles are concerned. WO92/09354 describes an acoustical chamber ensuring an agglomeration of small particles thus allowing to collect thereafter the agglomerated particles by classical means conceived for larger size particles. In order to ensure efficiency, the transfer time of the particles through the acoustical chamber must be relatively long thus requiring a chamber of large dimensions and therefore a very high acoustical energy.
U.S. Pat. No. 2,535,679 discloses an agglomeration method for aerosol particles in an acoustical chamber according to which a portion of the outlet flow of the acoustical chamber is fed back to its inlet in order to increase the probability of collisions between particles of the aerosol.
A similar feed-back is also proposed in U.S. Pat. No. 4,378,976 but in this case a filtered flow is selected for the feedback which practically does not contain any more agglomerated particles.